From 69b89fb46df3b2b0ab189218812efdcf5852f8f2 Mon Sep 17 00:00:00 2001
From: Alex Auvolat <alex@adnab.me>
Date: Tue, 26 Oct 2021 19:13:41 +0200
Subject: Fix race in block resync

---
 src/model/block.rs | 17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/src/model/block.rs b/src/model/block.rs
index 35d3871a..08002911 100644
--- a/src/model/block.rs
+++ b/src/model/block.rs
@@ -12,7 +12,7 @@ use tokio::io::{AsyncReadExt, AsyncWriteExt};
 use tokio::sync::{watch, Mutex, Notify};
 
 use garage_util::data::*;
-use garage_util::error::Error;
+use garage_util::error::*;
 use garage_util::time::*;
 use garage_util::token_bucket::TokenBucket;
 
@@ -28,7 +28,7 @@ use crate::garage::Garage;
 /// Size under which data will be stored inlined in database instead of as files
 pub const INLINE_THRESHOLD: usize = 3072;
 
-pub const BACKGROUND_WORKERS: u64 = 2;
+pub const BACKGROUND_WORKERS: u64 = 1;
 
 const BLOCK_RW_TIMEOUT: Duration = Duration::from_secs(42);
 const BLOCK_GC_TIMEOUT: Duration = Duration::from_secs(60);
@@ -393,8 +393,7 @@ impl BlockManager {
 	}
 
 	async fn resync_iter(&self, must_exit: &mut watch::Receiver<bool>) -> Result<(), Error> {
-		if let Some(first_item) = self.resync_queue.iter().next() {
-			let (time_bytes, hash_bytes) = first_item?;
+		if let Some((time_bytes, hash_bytes)) = self.resync_queue.pop_min()? {
 			let time_msec = u64_from_be_bytes(&time_bytes[0..8]);
 			let now = now_msec();
 			if now >= time_msec {
@@ -404,9 +403,9 @@ impl BlockManager {
 					warn!("Error when resyncing {:?}: {}", hash, e);
 					self.put_to_resync(&hash, RESYNC_RETRY_TIMEOUT)?;
 				}
-				self.resync_queue.remove(&time_bytes)?;
 				res?; // propagate error to delay main loop
 			} else {
+				self.resync_queue.insert(time_bytes, hash_bytes)?;
 				let delay = tokio::time::sleep(Duration::from_millis(time_msec - now));
 				select! {
 					_ = delay.fuse() => {},
@@ -453,7 +452,7 @@ impl BlockManager {
 					&self.endpoint,
 					*to,
 					msg.clone(),
-					RequestStrategy::with_priority(PRIO_NORMAL)
+					RequestStrategy::with_priority(PRIO_BACKGROUND)
 						.with_timeout(NEED_BLOCK_QUERY_TIMEOUT),
 				)
 			});
@@ -461,7 +460,7 @@ impl BlockManager {
 
 			let mut need_nodes = vec![];
 			for (node, needed) in who.iter().zip(who_needs_resps.into_iter()) {
-				match needed? {
+				match needed.err_context("NeedBlockQuery RPC")? {
 					BlockRpc::NeedBlockReply(needed) => {
 						if needed {
 							need_nodes.push(*node);
@@ -482,14 +481,14 @@ impl BlockManager {
 					need_nodes.len()
 				);
 
-				let put_block_message = self.read_block(hash).await?;
+				let put_block_message = self.read_block(hash).await.err_context("PutBlock RPC")?;
 				self.system
 					.rpc
 					.try_call_many(
 						&self.endpoint,
 						&need_nodes[..],
 						put_block_message,
-						RequestStrategy::with_priority(PRIO_NORMAL)
+						RequestStrategy::with_priority(PRIO_BACKGROUND)
 							.with_quorum(need_nodes.len())
 							.with_timeout(BLOCK_RW_TIMEOUT),
 					)
-- 
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